Linux is much more popular on Servers than Desktops. Windows dominates the desktop and laptop OS as the market declines. Android and iOS are the dominant mobile OS on tablets and phones. The Internet of Things will have OSs in all the different devices from a wide range of suppliers. It may have been a dream of OS focused executives to dominate with an OS across devices, but with device counts now reaching billions the General Purpose Operating System that created the opportunities for DOS, Windows, and Linux needed by customers has reached its limits.
The problem is the larger the market share the harder it is to develop and test new OS releases which slows down the overall hardware development. No one will accept an OS that slows hardware development.
It was not too long ago when users would talk about running a version of Windows or Mac OS. Smartphones and Tablets are with people more and people talk about the device brands more the OS brands. The developer audience will talk about a version of the OS, but end users less and less.
Being an old OS guy working on Mac OS and Windows OS (I stopped working on desktop OS with Windows XP and moved to Windows Server 2003, then stopped completely) looking at OS development is still interesting, but I don't want to work on them full time any more. Which in some ways gives a perspective to watch from afar.
The OS is simply part of the overall solution and not as important as it was. The user interface is what people interact with not the low level OS which is hidden much to the frustration of those who want to create a general purpose operating system across all devices. Linux on the server appeals to those who don't' want to be bothered with a user interface. The servers is where there is still the battle for general purpose OS between Windows and Linux but there are much less people working on server OS than mobile OSs.